You don't need an advanced IDE to write PHP programs, but if you cut wood it can be more effecient to use a chainsaw than a traditional saw. And if the only tool you have is a hammer, everything soon starts to look like a nail. Embarcadero's former Borland's Dephi RAD IDE that is also available for C++ (see the C++ sub forum) is now available for PHP.

is the link where you can download a PDF document with a great introduction to the IDE.

PHP 6 is still not finished. But the important concept of namespaces is implemented in PHP 5.3.x. The rumours say that the reason why PHP 6 takes so long to finish is the support for unicode. If you wan't to get a flying start of PHP 6 and unicode development you can start here: